It is well known to use an inflatable cuff to control blood flow into a subject's limb for a brief period in order to estimate the subject's blood pressure, and to occlude blood flow into a limb for an extended period to provide a bloodless surgical field in the portion of the limb distal to the cuff. When employed to provide a bloodless surgical field, occlusive cuffs constitute one element of a surgical tourniquet system (hereinafter called a "tourniquet"). Tourniquets typically include the following basic elements: a source of pressurized gas, an inflatable cuff for encircling a limb at a selected location, and a pressure-regulating mechanism for controlling and maintaining the pressure of gas in the inflatable cuff, and thus the pressure applied by the cuff to the limb which the cuff encircles.
The recent advent of electronic tourniquets which employ digital technology in the regulation of pressure has led to significant improvements in the safety and accuracy of surgical procedures performed with an occlusive cuff applied proximally on a limb portion. These systems allow the surgeon to safely maintain a constant pressure on the limb which he estimates to be near the minimum required to safely occlude blood flow into the limb ("limb occlusion pressure"). However, similar improvements have yet to be largely realized in surgery of the isolated digit, i.e. in surgery of the finger or toe where such surgery is performed in conjunction with a tight band applied proximally on the digit to occlude blood flow into the digit. This lack of improvement in prior-art devices and techniques has persisted, despite an increasing frequency of surgery on the isolated digit due to reduced anesthetic risk and reduced complexity in comparison to alternate procedures involving anesthetizing a complete limb or the entire patient. Procedures involving surgery of the isolated digit at present include: suturing of lacerations, dry-field explorations for foreign bodies, open reductions of fractures, repairs of tendons, incisions and drainage of infected pulp spaces, and fusions of arthritic proximal interphalangeal and distal interphalangeal joints. At present, for example, it is estimated that more than 250,000 surgical procedures may be performed annually on isolated digits by orthopedic, plastic and trauma surgeons.
For surgery of the isolated digit, occlusion of blood flow is typically achieved by a 0.25-inch latex rubber tube known as a Penrose drain which is drawn tightly around the base of the proximal phalanx and secured with an hemostat, or by the use of a Penrose drain in the fashion of a miniature Esmarch bandage, or by the use of a finger from a surgical glove that is opened at the tip and rolled onto the finger from the distal to proximal end in order to exsanguinate the digit and leave a tight band at the base of the proximal phalanx. Some specific complications associated with these prior-art devices have been reported, and it has been suggested that the actual complication rate is much higher than the incidence of case reports in the literature. The devices which are commonly used for occluding blood flow into the digit have a number of problems and hazards associated with them. First, the actual pressure exerted on the digit may vary widely among surgeons having different application techniques, and among digits of differing circumferences, and may be considerably higher or lower than the minimum pressure required to occlude blood flow into the digit ("digit occlusion pressure"). Both excessively high pressures and excessively low pressures may be hazardous. One recent study found that occlusive pressures generated by rolled surgical gloves ranged from 113 to 363 mmHg, while pressures generated by Penrose drains exceeded 800 mmHg. Another recent study showed that the pressure beneath a 0.25-inch Penrose drain used as an occlusive band varied between 100 mmHg and 650 mmHg, and that the pressure generated beneath a rolled glove finger varied from 120 mmHg to more than 1000 mmHg.
A second disadvantage of common techniques for occluding blood flow into digits is that the pressure in the occluding band cannot be adjusted accurately or reliably by the surgeon intra-operatively; the inability to increase pressure intra-operatively may promote the use of techniques which routinely generate higher pressures than required in many instances.
A third disadvantage of commonly used techniques for occluding blood flow into digits is that the surgeon cannot release and re-establish occlusive pressure readily if desired during a procedure. This may adversely affect the nature and quality of some surgical procedures, because the surgeon cannot easily release pressure, evaluate the effect of blood flowing into the surgical site, and then re-establish a bloodless field in order to continue with the procedure.
A final disadvantage is that current methods do not permit the surgeon to monitor the pressure actually applied to the digit, so that the surgeon can relate hazards, incidents and unexpected clinical outcomes to applied pressures, and thus take appropriate remedial action if warranted during subsequent procedures.
A prior-art pneumatic cuff for use on digits has been described in the literature (see C. P. Tountas, "A disposable pneumatic digital tourniquet," J. Hand. Surg. Vol. 11A, 1986, pp. 600-601), although this prior-art cuff is not in widespread use. The prior-art pneumatic device consists of a mini-bladder held about a digit with hook and pile material, and is connected to a syringe, whose air can be compressed and held by a spring housing. Two markings are given on the barrel of the syringe so that the plunger may be depressed to either of these two markings to compress air in an attempt to generate one of two arbitrary pneumatic pressures in the cuff as it encircles a digit. This prior-art device has significant limitations which restrict its utility and which prevent significant improvements in safety from being achieved clinically. First, it has been found in work which led to the present invention that the minimum occlusion pressure for digits, i.e. the digit occlusion pressure, varies according to the digit circumference for a cuff of a specified width and design; with the prior-art pneumatic cuff the digit occlusion pressure will vary widely as a function of digit circumference, and the cuff does not allow for estimation of the digit occlusion pressure when the cuff encircles a particular digit. The pressure established by depressing the barrel of the syringe in the prior-art pneumatic cuff system will be rather arbitrary and will likely be significantly higher or lower than the digit occlusion pressure. Second, the degree to which the air in the prior-art pneumatic system must be compressed by depressing the plunger of the syringe in order to achieve some arbitrary pressure depends upon the snugness with which the cuff was initially applied to the digit and also depends upon the extent to which segments of the mini-bladder of the cuff overlap as they encircle the digit. Third, the prior-art pneumatic cuff has a significant discontinuity at the cuff/digit interface caused by overlapping of thick cuff segments, which results in variations in applied pressure over a localized area. Fourth, the prior-art pneumatic cuff has only one means of securing the cuff around a digit, which may be hazardous at high pressures in that the event that the securing means becomes ineffective. Fifth, the prior-art pneumatic cuff will remain pressurized to a constant pressure only if there are no leaks in the system. In practice leaks occur, especially at the connection between the syringe and the cuff. The prior-art pneumatic cuff is not able to compensate for such leaks, and so in the presence of leaks the pressure will decrease to a hazardous level and permit blood to flow into the surgical site. The prior-art pneumatic cuff provides for no monitoring of the actual pressure in the cuff by pressure sensing means. Also, the prior-art pneumatic cuff allows for no precise regulation of pressure to maintain the pressure in the cuff near a desired pressure for the duration of a surgical procedure, or to allow for controlled blood flow at certain times during the surgical procedure if desired by the surgeon, or to allow for adaptation of the cuff pressure in response to changes in the patient's blood pressure. Finally, the prior-art pneumatic cuff contains no alarm means to warn the surgeon in the event of a hazard such as loss of pressure.
One of the limitations of the prior-art pneumatic cuff for digits described above illustrates a problem common to all prior-art pneumatic cuffs which are intended for use on limbs. At present, a variety of pneumatic cuffs of different designs, including differing widths, circumferences, shapes and materials, are manufactured for use on limbs as occlusive cuffs. These cuffs do not enable the surgeon to estimate reliably the minimum constant pressure normally required to safely occlude blood flow over a time period suitably long for the performance of a surgical procedure in a limb encircled by a particular cuff which he chooses. Instead, many surgeons presently set cuff pressures rather arbitrarily, without adequately taking into account the circumference of the patient's limb at the cuff site and pertinent characteristics of the design of the specific cuff employed, including the width of the cuff. This can be hazardous because the minimum constant pressure which must be established in a cuff encircling a portion of a limb to safely occlude blood flow distal to the cuff for the duration of a surgical procedure is dependent on variables including the circumference of the limb at the cuff site and specific characteristics of the design of the cuff employed, especially with respect to its width and shape, as well as being dependent on significant fluctuations in systolic blood pressure which normally occur in anesthetized subjects over the time period of a surgical procedure. Methods have been described in the prior art to assist surgeons in estimating limb occlusion pressures as a function of limb circumferences. However, these methods do not take into account the significant differences in characteristics among different cuffs, and require the surgeon to measure the circumference of a limb at the cuff site, and then to refer to a separate graph for estimating the limb occlusion pressure; these methods are impractical and error-prone due to the difficulty of accurately measuring the circumference of a limb at the prospective cuff site prior to cuff application and surgery, due to wide variations in the snugness of initial cuff application and thus the effective cuff circumference, and due to errors which may arise in interpolating using a separate graph to estimate occlusive pressure. Also, most significantly, the separate graphs on which these methods are based may have been obtained using cuffs of much different design than the cuff to be employed by the surgeon, and hence the pressure/circumference relationship employed may not be accurate for that cuff. Also, the graphs on which these methods are based may have been based on cadaver studies or studies of a small number of subjects not similar to the patient undergoing surgery.
The applicant is aware of the following United States patents which are more or less relevant to the subject matter of the applicant's invention.
______________________________________ 4,605,010 8/1986 McEwen 128/686 4,479,494 10/1984 McEwen 128/327 128/682 4,469,099 9/1984 McEwen 128/327 128/682 4,308,871 1/1982 Shouda 128/686 3,812,844 5/1974 Sokol 128/2.05G, 128/2.05C 3,765,405 10/1973 Natkanski 128/2.05C 3,756,239 9/1973 Smythe 128/327, 128/2.05C 3,699,945 10/1972 Hanafin 128/2.05C, 128/327 3,670,735 6/1972 Hazlewood 128/327 3,633,567 1/1972 Sarnoff 128/2.05C, 128/327 3,587,584 6/1971 Keller 128/327 3,570,495 3/1971 Wright 128/327 3,504,675 4/1970 Bishop 128/327 3,095,873 3/1961 Edmunds 128/2.05 2,468,133 4/1949 Sullivan 128/327 2,031,870 2/1936 Vertuno 128/327 ______________________________________
The applicant is also aware of the following published reference which are more or less relevant to the subject matter of the applicant's invention.
J. A. McEwen and R. W. McGraw, "An adaptive tourniquet for improved safety in surgery." IEEE Transactions in Bio-Medical Engineering, Vol. BME-29, February 1982, 122-128. PA0 J. A. McEwen and G. F. Auchinleck, "Advances in surgical tourniquets," J. Assn. Operating Room Nurses, Vol. 36, 1982, pp. 889-896. PA0 J. A. Shaw and D. G. Murray, "The relationship between tourniquet pressure and underlying soft-tissue pressure in the thigh." The Journal of Bone Surgery, Vol. 64-A, 1982, pp. 1148-1152. PA0 A. C. McLaren and C. H. Rorabeck, "The pressure distribution under tourniquets." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 433-438. PA0 R. J. Newman and A. Muirhead, "A safe and effective low pressure tourniquet." Journal of Bone and Joint Surgery, Vol. 68-B, 1986, 99. 625-628. PA0 J. A. Shaw, W. W. Demuth, and A. W. Gillespy, "Guidelines for the use of digital tourniquets based on physiological pressure measurements." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 1086-1090. PA0 J. D. Lubahn, J. Koeneman and K. Kosar, "The digital tourniquet: How safe is it?" J. Hand Surg., Vol. 10A, 1985, pp. 664-669.